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For nuclear reactions spectroscopy, we are particularly interested in two f irmware packages dedicated to DPP: PSD and PHA. Both are available in MARS. The PSD firmware allows for integrating incoming pulses and producing an energy spectrum. The selection of events can be done by means of a leading edge discriminator (LED) or a constant fraction discriminator (CFD). It features a double gate integration of the input in order to calculate the PSD factor, given by:

where Qlong and Qshort are the integrated charges in the long and short gates (Figure 2a). It represents the ratio between the signal tail and the total inte gral. PSD is suitable for processing pulses with fast decay time, such as those produced by electrons, gammas, and neutrons in scintillation detectors [24]. The PHA firmware allows the digitizer to obtain an energy spectrum by applying a trapezoidal filter to the input pulse. It transforms the typical expo nential decay pulse, generated by a detector (and transmitted through a pream plifier), into a trapezoidal signal whose height is proportional to the input pulse amplitude. The height of the trapezoid is measured at the peaking time (see Figure 2b). This firmware is ideal for processing pulses with long decay times, such as those produced by alphas and heavy ions in semiconductor detectors [24]. This is the case for charged fragments resulting from nuclear reactions. Therefore, we will report on the PHA firmware from now on.

Figure 3: Scheme of the setup used for MARS characterization.

3. MARS characterization

As a proof of concept and validation, MARS has been firstly tested in a laboratory environment. Figure 3 schematize the first setup used to characterize the MARS electronic system. The test pulses were generated by the 419 ORTEC precision pulse generator [25] or the digital detector emulator DT4800 [26]. Both modules allow for emulating electronic pulses that simulate the detection of a charged particle in a silicon detector. The former works at a fixed frequency of 70 ± 10 Hz [25], while the latter can be set to different values. The DT4800 allows for emulating pulses with time and amplitude follow ing Poisson distributions. It allows for loading spectra from different sources, simulating their emission rate and pulse height distribution. It also allows for modifying the rise and decay times of the pulses. It is worth mentioning that pulses were initially delivered through the com monTESTIN (input) of A1422 preamplifiers. In practice, the electronic signals, coming from detectors, must be transmitted through individual DET IN elec tronic chains. However, unlike DET IN, TEST IN has a 50 Ω termination in series with a 1 pF capacitance. Further measurements were performed using a triple alpha source placed in front of detectors, which were then connected to individual A1422 DET IN. According to Figure 3, MARS system is divided into 8 individual electronic chains (1- 8) related to each A1422 (13323 and 13324) preamplifier and 16 data acquisition (DAQ) chains (0- 15) related to the V1725S digitizer. These numbers coincide with the numbers printed, respectively, in the front panel of A1422 preamplifiers and V1725S digitizer.